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HIV test indeterminate due to flu infection?
Oct 31, 2009

Hi Bob

I went to the doctor feeling crook on Tuesday, muslce aches, freezing, turned out I had 39 degrees C temperature. The doctor prescribed Tamiflu and requested a blood test (HIV and full blood count). I picked up the Tamiflu from the Chemist straight away and took one pill, then I went to the pathology centre for the blood test about half an hour later. Wed/Thu were hell, but today I'm up again and feeling much much better.

The full blood count came back normal, but today, Friday, I was told that my HIV test result is indeterminate so far and the lab wants to do further tests and I have to wait another week. I read about the reasons that can cause indeterminate test results (such as a person is seroconverting right now), and I am freaking out. So I wanted to check with you if the flu, or swine flu, or taking Tamiflu can specifically cause an indeterminate result?

Response from Dr. Frascino

Hello,

Tamil will not affect the accuracy of HIV test results. However, having the flu or getting flu vaccinations might in rare instances induce cross-reacting antibodies, which could lead to an indeterminate (or even false-positive) result. (See below.) These falsely positive or indeterminate results are generally quickly sorted out by means of follow-up testing.

Dr. Bob

The Flu and False Positve HIV Results (FLU SHOT AND FALSE POSITIVE HIV TEST) Mar 31, 2008

I was reading your archives and came across a question about the correlation between false positive HIV results and the Flu shot and you said this was false in 2005 but The New England Journal of Medicine printed an article in 2006 presenting the evidence of this Correlation. I was just wondering because my partner has recently tested indeterminate and then positive. The doctor used the same sample for each screening, but he then tested indeterminate again in a different test the following week. I've tested negative twice and we haven't had sex in the past 4 months. Before that time we have been strictly monogamous and have had unprotected sex for the two years before this strictly with each other. I know the window is six months before you can be considered HIV-negative, but that it is extremely rare that it takes that long. I'm just very confused as to how he could be positive and I could be negative when we were not protected for 2 years and hundreds of times having intercourse. I've also seen a couple places that stated that immuno diseases such as diabetes can cause false positives. He has been diabetic since age 5 and is now 28. Thanks for your help!

Response from Dr. Frascino

Hello,

Yes, influenza vaccine can cause a false-positive HIV-antibody test due to nonspecific cross-reacting antibodies. I have written about this multiple times over the past several years. (See below.) Your partner has had one positive and two indeterminate HIV tests. You don't mention the type of screening test, ELISA or ELISA plus confirmatory Western Blot. I would suggest your partner repeat his ELISA and if it's repeatedly reactive (positive), he should get a Western Blot test. If negative, he's HIV negative. End of story. If positive, he's HIV positive and should see an HIV specialist for additional evaluation. If he tests indeterminate again, I would recommend getting a follow-up HIV DNA PCR qualitative test to help sort out this unclear result. If indeed he has had essentially no HIV risks, there should be no reason for him to be HIV positive. You can read more about indeterminate HIV tests in the archives.

If your partner is HIV positive, you should have HIV tests at both the three- and six-month marks from the date of your last potential exposure.

Good luck to you both.

Dr. Bob

Gardasil plus flu vaccine, false positive HIV?(INFLUENZA VACCINATION AND INDETERMINATE WESTERN BLOT TESTS) (FLU SHOT AND FALSE POSITIVE HIV TESTS) Dec 15, 2007

A week ago my 17-year-old daughter received a letter from Red Cross indicating she screened HIV positive after donating at a recent blood drive. Results were HIV-1/HIV-2 Positive, Confirmatory Indeterminate, NAT Negative. Retesting was done at a hospital lab. Results are HIV (weak) negative and we await Confirmatory results. My daughter appears to have no risk factors. She is a virgin, has no history of sexual activity whatsoever, no tattoos, no IV drug use. Ten days before the blood donation she received (her first ever) flu vaccine and also the second of three Gardasil shots. She was also prescribed Provera a month earlier. After reading previous posts I believe you draw no correlation between vaccines and false positive HIV tests, however there does seem to be recent information to the contrary. Information published in March 2006 in the New England Journal of Medicine asserts recent inoculation with any brand of influenza vaccine was significantly associated with a false positive screening assay for HIV antibodies. Guidelines of both Johns Hopkins and the New York State Department of Health list influenza vaccination as a known cause of indeterminate results on Western blotting for HIV antibodies. Given the escalating international awareness of various influenza strains, it is very important to remind patients and clinicians that influenza vaccination may cause cross-reactivity with HIV antibody assays. I'm not qualified to debate the validity of this information, but it is somewhat comforting for a family in a situation like ours to think that a vaccine might be the issue. My question: What is your opinion of the likelihood of an HIV positive confirmation considering my daughters history? Thank you.

Response from Dr. Frascino

Hello,

Thanks for your post. Yes, we are trying to get this more recent information out to a wider audience. The influenza vaccine changes from year to year to cover the most likely flu strain candidates for the coming flu season. We do have recent information that flu vaccination can cause some degree of nonspecific cross-reacting antibodies, which can confound HIV-antibody tests. Generally speaking, these cross-reacting antibodies cause "indeterminate" rather than "false positive" HIV tests. Please note a reactive ELISA with subsequent indeterminate Western Blot is considered to be an "indeterminate" HIV test result, not a positive test! HIV testing center and certainly HIV specialists are well aware of these potential complicating factors and we have methods for sorting out serological results that are either in dispute or indeterminate.

In your daughter's case of essentially no potential HIV exposure and a recent flu vaccine, you can rest assured her indeterminate Western Blot is not related to HIV seroconversion, but rather to the detection of cross-reacting antibodies. That her NAT was negative confirms this fact, because NAT testing does not rely on antibody detection.

Happiest Holidays to you and your entire family.

Dr. Bob



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